Inkjet printing apparatus of the type in which this invnetion is intended to be utilized produce a plurality of uniform drops aligned parallel to one another and perpendicular to the movement of paper or other material on which printing is to occur. The printing is achieved by using a reservoir of printing fluid such as ink, with a plurality of aligned orifices in one surface of the reservoir. The ink is ejected through these orifices at a predetermined rate and is stimulated in such a manner that uniform drops of ink are formed at the ends of filaments of ink which issue from the orifices. A series of charge electrodes are positioned adjacent the points of drop formation and are connected to sources of charging control voltage, so that corresponding electrical charges are induced upon the drops at their respective times of formation. The drops then pass through an electrical deflection field that causes drop deflection in correspondence with the applied charges. Uncharged drops may be directed onto an appropriately positioned catcher.
Alternatively, drops charged above some predetermined level may be directed onto the catcher. The remaining drops reach the medium upon which printing is to occur to carry out the printing function.
Economical methods of forming the orifices in an orifice plate or holes in a charge plate are difficult to establish since the nature of the system requires the use of extremely small diameter holes in these plates. For example, the orifices in a typical orifice plate are generally in the range of 0.0005 to 0.0015 inches in diameter, and the holes in a typical charge plate are generally in the range of from 0.005 to 0.010 inches in diameter.
It has been recognized that orifice plates for inkjet printing apparatus may be fabricated from glass tubes aligned to form a uniform array of orifice nozzles as, for example in Cone U.S. Pat. No. 4,112,436 or Humenik U.S. Pat. No. 4,122,460. However, the major problem in implementing this fabrication step resides in aligning, supporting and bonding the glass tube in place. For example, Cone teaches etching parallel V grooves in a silicon wafer which is then split to form a pair of support wafers. The wafers are secured to a frame having an underlying glass plate in spaced relation in a horizontal plane, and glass fibers are positioned in the grooves. Resin is then poured over the fibers and fills the spaces between the fibers and the underlying glass plate. A second glass plate is placed over the epoxy and the assembly is clamped with glass plates to form a sandwich. The epoxy is cured and the assembly is sliced orthogonally to form thin nozzle array sections. However, the difficulty with using the approach that because V grooves are used to support the glass fibers, only a limited number of points of contact exist between the fibers and the substrate. Moreover, the flow of epoxy over the surface of the fibers may be uneven, resulting in a weak assembly.
In an alternative approach, disclosed in Dressler, U.S. Pat. No. 4,429,322, the glass fibers are aligned in a mold and a molding compound is poured over and around the fibers and permitted to cure. In another approach disclosed in the same patent, the fibers are aligned in parallel spaced relationship on a glass or ceramic substrate using double faced adhesive tape to hold the fibers in position while ceramic paste is applied. After heating to cure the ceramic paste, the solder glass frit is dusted over the fibers and compacted with ultrasonic vibration. A cover plate of glass or ceramic is positioned and the assembly is heated to seal the fibers. Again, a weak assembly results because of the lack of contacting support between the substrate and the fibers, and the likelihood of the formation of gaps or bubbles where the tape epoxy or frit does not flow, because of the extremely small diameters being used for the glass nozzles.
Another approach is shown in Hoffman, U.S. Pat. No. 4,019,886, where a plurality of glass nozzles are shown in FIGS. 1A and 1B aligned in channels, with the spacing being fixed essentially by the diameter of the elements. Again, serious problems result from lack of alignment between the fibers, and the inablity to flow the epoxy or other sealing material evenly over the fibers.